Preparation And Properties Of CdTe/CdS Quantum Dots And Their Composites

As semiconductor with fluorescence properties. Quantum dots (QDs) possess many advantages such as narrower emission spectra, tunable maximum emission wavelength with changeable sizes and compositions, high brightness, long fluorescence compared to conventional organic dyes. With these properties QDs are playing a more and more important role in the emerging science and traditional field such as biological imaging, photoelectric conversion, optical display and analysis. Up to now, we still need to improve the luminous efficiency, hydrophily and stability. In this paper, water-soluble CdTe/CdS quantum dots were synthesized by hydrothermal method, and the quantum dots were assembled into organic and inorganic medias to prepare a series of bulk and micro/nano materials with morphology easily controlled. The content of the paper mainly includes:(1) The synthesis and property of CdTe/CdS in aqueous solution. A simple method was developed to prepare water-soluble CdTe QDs with one step direct hydrothermal method by using the materials of Na2TeO3as Te source reduced by NaBH4and carboxylic acid molecules were used as stabilizers. Different size water-soluble CdTe quantum dots with different fluorescent were synthesized by controlling reaction time. Concentration of precursor, pH of precursor, and reaction temperature are important in the preparation of CdTe QDs. Based on these results, we found that low precursor concentration and high reaction temperature were helpful to improve the growth rate of quantum dots and full width at half maximum (FWHM) narrowing of fluorescence of CdTe QDs. When the concentration of precursor is1X10-3mol/L, react at180℃with pH=9, the quantum yields (QY) of CdTe QDs are up to65%without any post-treatment. QDs epoxy resin composites bulk materials were prepared through phase transfer of CdTe QDs. Use the same hydrothermal method we prepared CdS QDs and the structure and fluorescence characterized of CdS QDs were studied.(2) Shape-controlled synthesis and property of CdS-Cystine Composite. CdS-cystine composite were synthesized by coprecipitation method, using CdS QDs and L-cysteine as raw material. The morphology of the composite was easily controlled by changing the concentration of L-cysteine and the pH value of the solution. Moreover the formation mechanism of the composite materials was preliminary discussed. As L-cysteine is the biological essential amino acids. CdS-cystine composite not only improves the stability of the quantum dots but also enhances its biological compatibility.(3) Self-assembly synthesis and luminescence property of CdTe-Gd(OH)CO3micro/nanotubes (CGON). Cooperating with previous work in our workshop, cation exchange was explored as a generic approach to assemble CdTe QDs into the shell of Gd(OH)CO3nanotubes without toxic solvents, surfactant and etchant in a moderate condition. Cation exchange reactions were often carried out in the phase interface, a large difference in solubility provides the driving force for the ion replacement. Generally, the starting material present in a solution containing an appropriate precursor will spontaneously undergo cation exchange to yield the product with a lower solubility. On the other hand, using bifunctional linker coupling method, CdTe QDs are tethered to the surfaces of MgCO3·3H2O template through bifunctional molecular linkers which have two functional ends, thiol and carboxyl. Thiol binds strongly to the surface of Cadmium telluride nanocrystal. the other end of the carboxyl group firmly binds to the surface of MgCO3·3H2O, which can improve self-assembly of CGON. These new fluorescent composite materials are demonstrated as fluorescent Pb2+probes.